1. Field
One embodiment of the present invention relates to a disk drive, and in particular, to a head positioning control technique using spiral servo patterns.
2. Description of the Related Art
In general, in disk drives typified by hard disk drives, servo patterns (servo data) used for head positioning control are recorded on a disk medium that is a data recording medium. The disk drive uses the servo patterns read by the head to controllably place the head at a target position (target track) on the disk medium.
The servo patterns recorded on the disk medium are concentric servo patterns having a plurality of servo sectors normally arranged circumferentially at a fixed interval so as to constitute concentric servo tracks.
The concentric servo patterns are recorded on the disk medium by a servo writing step included in a disk drive manufacturing process. A proposal has been made of a method of recording a plurality of spiral servo patterns constituting base patterns (seed patterns) on the disk medium during the servo writing step (see, for example, U.S. Pat. No. 6,987,636 B1).
In the servo writing step in accordance with the proposed method, a plurality of spiral servo patterns (a multi-spiral servo pattern) are recorded, by, for example, a dedicated servo track writer (STW), on the disk medium not incorporated yet into a disk drive to be shipped as a product. The disk medium is subsequently incorporated into the disk drive, which performs a servo self-write method to write concentric servo patterns used for the product, to the disk medium.
A normal disk drive uses a read head that reads the servo patterns from the disk medium and a write head that writes servo patterns to the disk medium; the read head and the write head are separately mounted in the disk drive. The width of the read head is relatively small compared to that of the write head. Thus, the waveform of burst signals reproduced from the spiral servo patterns read from the read head is hexagonal. In U.S. Pat. No. 6,987,636 B1, the burst signal waveform is processed as a rhombic signal.
In the disk drive to be shipped as a product, the concentric servo patterns are written to the disk medium as described above. To allow the write head to write the concentric servo patterns to the disk medium, positioning of the head is controlled on the basis of the spiral servo patterns read by the read head. The disk drive controls the positioning of the head by calculating an error in the position of the head on the basis of the servo burst signals reproduced from the concentric servo patterns.
However, the waveform of burst signals reproduced from the spiral servo patterns is hexagonal. Consequently, a scheme (algorithm) of calculating an error in the position of the head in the disk drive is not applicable directly to the head positioning control. The method in U.S. Pat. No. 6,987,636 B1 processes the burst signal waveform as a rhombic signal and thus allows the position error calculating scheme to be partly applied to the head positioning control. However, the method is disadvantageous in a practical sense in that the method processes the burst signal waveform as a rhombic signal and fails to completely apply the position error calculating scheme to the head positioning control.